[darwinbuild] -depsbuild going away soon...

[Shantonu Sen]

-depsbuild was/is an option to load binary roots using another  
(typical older) build than the "current" build, for instance to allow  
8A428 to provide roots when building projects from the 8B15 plist.  
Darwinbuild 0.7.1 supports a more sophisticated mechanism where if  
the "current" build doesn't have a binary root, the build inheritance  
tree is traversed to satisfy the root, which should remove the need  
for explicit -depsbuild. Indeed, it's not clear how -depsbuild would  
interact with this new code anyway.

I plan on removing this option soon. If you've been using -depsbuild,  
try not using it. Things should work equivalently, if not better.

Shantonu